#include <stdio.h>
#define N 10000
main() {
  int i, p, q, t, id[N];
  for (i = 0; i < N; i++) id[i] = i;
  while (scanf("%d %d\n", &p, &q) == 2) {
    if (id[p] == id[q]) continue;
    for (t = id[p], i = 0; i < N; i++)
      if (id[i] == t) id[i] = id[q];
    printf(" %d %d\n", p, q);
  }
}
